1. Field of the Invention
The present invention relates to a surface emitting laser, and more particularly a method for fabricating a Bragg reflector with a uniform thickness in which the thickness of a growing epitaxial layer is effectively controllable by means of an in-situ laser reflectometer which employs a laser beam having the same wavelength as that of the Bragg reflector to be fabricated.
2. Description of the Related Art
Metal-organic chemical vapor deposition (hereinafter, referred to as MOCVD) which is a common method for growing a semiconductor multilayer structure has been widely used for growing an epitaxial layer with an electron and photon structure on a GaAs or InP substrate.
Unlike a conventional laser diode which generates the laser beam at the sides, a recently developed surface emitting laser (hereinafter, referred to as SEL) generates the laser beam at the surface. It is well known that such a SEL has the advantages of a low threshold current and a high emitting efficiency. It is therefore expected that the SEL will become a promising laser emitting device in the future. In general, the performance of the SEL is mainly dependent upon the uniformity of thickness of a Bragg reflector which is employed as a basic structure of the SEL. Further, it is preferred that the Bragg reflector should be designed to have a thickness equal to a quarter of the desired wavelength in order to obtain the maximum reflectivity. Conventionally, however, such Bragg reflector has been grown by using an epitaxial growing device which can not precisely control the thickness of the growing epitaxial layer.
According to a known method for fabricating the Bragg reflector, while a single layer is being grown by using raw materials for the Bragg reflector, a thickness of the growing layer is measured by means of an electron microscope to evaluate therefrom a growing speed. Then, in accordance with the evaluated growing speed, the growing time corresponding to the desired thickness of the Bragg reflector is determined. However, since the growing system does not have completely reproducible characteristics due to the variation of the growing condition depending on the materials, it is difficult to grow the Bragg reflector with a uniform thickness. According to another known method for fabricating the Bragg reflector, a refractive index is first evaluated by using a real time laser beam analyzer and then, a growing speed of the Bragg reflector is determined during the growing process based on the evaluated retractive index. Then, in accordance with the growing speed, the thickness of the growing Bragg reflector is controlled. However, since this known method uses the refractive index in order to evaluate the growing speed, it is necessary to previously know the retractive index of the epitaxial layer. Therefore, it may not be possible to precisely grow Bragg reflector in real time without knowing the refractive index previously.